| Popis: |
Though biologists recognize that populations of Colorado River cutthroat trout have declined, the magnitude of the loss remains unquantified. We obtained information from state and federal biologists and from state databases to determine the current distribution and status of populations of Colorado River cutthroat trout. Recent population extinctions have been documented throughout this range. Hybridization with rainbow trout, nonindigenous cutthroat trout (those established or supplemented by stocking of genetically pure fish), and introgressed hatchery stocks has degraded many populations of Colorado River cutthroat trout. Only 26% of the remaming populations are believed to be genetically pure. Almost 45% of the remaining populations are at least partly sympatric with non-native trout species or hybridized hatchery stocks. Brook trout are the most common sympatric non-native species. Barriers (permanent, physical obstructions) to upstream migration are known to protect 27% of the indigenous populations from non-native stocks. Land management problems were inconsistently mentioned, but grazing and dewatering were the most frequently cited. As a consequence of these threats, the continued existence of Colorado River cutthroat trout is in doubt. Of the 318 waters, only 20 contain Colorado River cutthroat trout that are believed to be indigenous, genetically pure, allopatric above a barrier, and in a drainage not recently stocked. |
